相关疑难解决方法(0)

通过单击showBottomSheet弹出导航到另一屏幕的屏幕时，以下代码引发此错误。我不明白为什么会这样。

class _CheckoutButtonState extends State<_CheckoutButton> {
  final GlobalKey<ScaffoldState> _globalKey = GlobalKey();
  final DateTime deliveryTime = DateTime.now().add(Duration(minutes: 30));

  final double deliveryPrice = 5.00;

  @override
  Widget build(BuildContext context) {
    SubscriptionService subscriptionService =
        Provider.of<SubscriptionService>(context);
    CheckoutService checkoutService = Provider.of<CheckoutService>(context);
    return Container(
      height: 48.0,
      width: MediaQuery.of(context).size.width * 0.75,
      child: StreamBuilder(
        stream: subscriptionService.subscription$,
        builder: (_, AsyncSnapshot<Subscription> snapshot) {
          if (!snapshot.hasData) {
            return Text("CHECKOUT");
          }
          final Subscription subscription = snapshot.data;
          final List<Order> orders = subscription.orders;
          final Package package = subscription.package;
          num discount = _getDiscount(package);
          num price = …